It is known from my German patent No. 23 13 425 to connect duct parts in high-pressure gas installations by use of frame-like assembled profiles. These profiles are generally of L-section so that that they have flanges extending perpendicular to and parallel to the respective duct side walls. The ends of the duct part can be fitted into the latter flanges and then secured thereto.
The profiles are joined together at their corners by fitting the legs of angle pieces into the flange extending perpendicular to the respective duct side wall, with at least two corner pieces in a corner being joined or prestressed together by means of screws or the like. In this manner the optional seal between the perpendicular flanges as well as the optional seal in the corner region between the corner pieces can be clamped in place.
The corner pieces themselves can be made in accordance with my U.S. Patent applications Ser. Nos. 739,053 of Nov. 5, 1976 (now abandoned) and 870,720 of Jan. 19, 1978 (now U.S. Pat. No. 4,123,094) as simple flat iron elements with smooth legs and a corner region inset with respect to the legs. Since considerable forces must be brought to bear in the corner region by means of the mounting screws in order to hold the seal tight in this particular critical region, the flat iron pieces must be made relatively thick for stability, so that no excessively large bending or twisting can occur. This means that the corner pieces are relatively heavy and therefore have relatively high material and transport costs. Since this is a nass-produced article, these costs are particularly important.